The invention relates to the genetic manipulation of plants, particularly to the expression and regulation of GDP-mannose pyrophosphorylase in transformed plants.
Gums are derived from the seeds of plants which accumulate certain polysaccharides as storage polymers. They are capable of forming gels or highly viscous solutions at low concentrations in solvents and have many industrial applications. Because gums can absorb large quantities of water, they are used as food additives to provide texture, prevent ice crystal formation, maintain crispness and retain moisture.
Gums also have uses outside of the food industry. For example, gums are used in the textile industry as dyeing and printing aids; in the petroleum industry as drilling agents for petroleum and gas wells; in the paper industry as binders and hardeners; in the mining industry for separation of minerals from crude ores; in the explosive industry to thicken explosive slurries and as desiccants; and in the cosmetic industry to thicken shampoos and conditioners. A new and rapidly emerging area for gum use is the pharmaceutical industry where gums have been reported to have applications as soluble fibers that lower cholesterol and blood pressure; as weight loss facilitators; as aids for the controlled release of drugs; in improving the microflora of the digestive system; in lowering blood glucose; and for prolonging the release of sugar during strenuous physical exercise.
Industrial gums are currently prepared from bacteria or from plant seeds. The main sources of seed-derived industrial gums are the subtropical plants Guar (Cyamopsis tetragonoloba), Locust Bean or carob (Ceratonia siliqua), Tara (Caesalpina spinosa), and Fenugreek (Trigonella foenumgraecum). More than 70% of natural plant gum is produced from Guar and Locust Bean.
Seed-derived gums are classified into two main categories: galactomannans and xyloglucans. Galactomannan, a linear polymer of mannosyl residues, substituted to varying degrees by galactosyl residues, is a major constituent of the seeds of the leguminous plants Guar, Fenugreek and Locust Bean. The differences in the properties of the galactomannan gums are determined by the mannose:galactose ratio in the polymer, which ranges from a low of 2 in Guar to a high of 4 in Locust Bean. Locust bean gum is considered to be of the highest quality for industrial applications and is the most expensive of all the plant seed gums.
Another class of plant gums, xyloglucans, has not received much attention, perhaps due to the very low yield of the source plants. Xyloglucans are the predominant storage polymers in the seeds of Nasturtium (Tropaeoleum majus), Tamarind (Tamarindus indica), and Balsam (Impatiens balsamina). Xyloglucan consists of a linear glucan backbone substituted with xylosyl residues. The xylosyl residues may be substituted with galactosyl residues.
Due to the high cost of gum derived from the seeds of subtropical plants, it is desirable to engineer transgenic plants which over-produce the gums galactomannan and/or xyloglucan. The present invention provides compositions and methods for the overexpression of enzymes and substrates required for the synthesis of the gum galactomannan.
The synthesis of the gum galactomannan is catalyzed by the enzymes mannan synthase and galactosyl transferase, from the substrates GDP-mannose and UDP-galactose (FIG. 1). The formation of the substrate GDP-mannose, from mannose-1-phosphate and GTP, is catalyzed by the enzyme GDP-mannose pyrophosphorylase. The present invention provides compositions and methods for manipulating the levels of enzymes in the galactomannan biosynthetic pathway in order to regulate gum production in plants, plant cells and plant tissues.
Protein glycosylation is required for cell growth. GDP-mannose is a substrate for glycosylation of proteins. Therefore, down-regulation of GDP-mannose pyrophosphorylase will result in decreased levels of GDP-mannose and concomitant decreases in protein glycosylation. Thus, by down-regulating GDP-mannose pyrophosphorylase, cell growth may be inhibited. The present invention includes antisense nucleic acids for GDP-mannose pyrophosphorylase which have use in decreasing GDP-mannose pyrophosphorylase and GDP-mannose levels. Also provided are expression cassettes encoding truncated GDP-mannose pyrophosphorylase for reduction of GDP-mannose pyrophosphorylase levels by cosuppression. Such methods and compositions inhibit cell growth, and are therefore useful in the production of dwarf plants, including ornamental Bonsai type plants.
Thus, it is an object of the invention to provide nucleotide sequences encoding GDP-mannose pyrophosphorylase gene and related genes. The sequences are useful in transforming plants for expression of GDP-mannose pyrophosphorylase or the antisense RNAs thereof Such sequences find use in regulating the levels of GDP-mannose, a substrate for the formation of the gum galactomannan and for protein glycosylation. Expression cassettes comprising GDP-mannose pyrophosphorylases and antisense RNAs thereto, are provided. Additionally provided are plants, plant cells, and plant tissues.
The present invention discloses compositions and methods for the synthesis of the gum galactomannan in non-legume plants, plant cells and specific tissues, as well as for the increased expression in leguminous plants, plant cells and specific tissues. The methods involve modulation of the levels of enzymes in the galactomannan biosynthetic pathway. The synthesis of the gum galactomannan is catalyzed by the enzymes mannan synthase and galactosyl transferase, from the substrates GDP-mannose and UDP-galactose. The formation of the substrate GDP-mannose, from mannose-1-phosphate and GTP, is catalyzed by the enzyme GDP-mannose pyrophosphorylase.
The methods of the invention involve manipulating the pathway for gum production by over-expressing or up-regulating at least one enzyme in the biosynthetic pathway. By overexpression or up-regulation is meant causing an increase of 0.2-200 fold in the level of an RNA, enzyme or substrate in a transformed plant, as compared with the non-transformed plant. Preferably, the increase is 0.5-150 fold, and more preferably 1-100 fold. A key step in production of the gum galactomannan is providing an adequate supply of substrates, which include GDP-mannose and UDP-galactose. Thus, in particular the nucleotide sequence for maize GDP-mannose pyrophosphorylase is provided for use in priming gum production. It is recognized that if other enzymes in the galactomannan biosynthetic pathway are identified, they can be used to manipulate gum production or precursor accumulation in plants of interest.
Compositions also comprise antisense constructs for enzymes of the galactomannan biosynthetic pathway. Such compositions have use in down-regulating the levels of enzymes and/or substrates of the galactomannan biosynthetic pathway. When a plant carries a transgenic copy of an endogenous or foreign gene, both genes may be silenced. This phenomenon is termed cosuppression. Accordingly, constructs encoding are truncated enzymes of the GDP-mannose biosynthetic pathway, preferably encoding a truncated GDP-mannose pyrophosphorylase, are provided for use in cosuppression of the enzymes in the pathway. By down-regulation is meant causing a decrease of about 0.1-1000 fold, preferably about 1-500 fold, and more preferably about 5-100 fold, in a RNA, enzyme or substrate. In a preferred embodiment, compositions encoding antisense RNA to mRNA for GDP-mannose pyrophosphorylase are provided. Such compositions have use in decreasing levels of GDP-mannose, a substrate for protein glycosylation. The decrease in a substrate for protein glycosylation will result in the inhibition of cell growth or in cell death. By inhibiting cell growth, dwarf, miniature and bonsai plants may be produced.
The present invention is further drawn to compositions and methods for manipulating the levels of enzymes of the galactomannan biosynthetic pathway in plants, plant cells, and specific plant tissues. By enzymes of the galactomannan biosynthetic pathway is meant GDP-mannose pyrophosphorylase, mannan synthase and galactosyl transferase. It is recognized that as the galactomannan pathway is further elucidated, newly discovered galactomannan biosynthetic enzymes are included in the methods of the invention. Compositions are nucleic acids relating to genes encoding enzymes of the galactomannan biosynthetic pathway in plants, preferably to GDP-mannose pyrophosphorylase or GDP-mannose pyrophosphorylase-like genes. Preferably, the GDP-mannose pyrophosphorylase is native to maize or a leguminous plant. By native to maize or a leguminous plant is meant that the GDP-mannose pyrophosphorylase may be present in a naturally occurring or cultivated species of maize or a leguminous plant. Nucleotide sequences for a maize GDP-mannose pyrophosphorylase gene and the amino acid sequence for the GDP-mannose pyrophosphorylase protein encoded thereby are disclosed, as well as fragments and variants thereof. These sequences are set forth in SEQ ID NOS:1 and 2. The maize GDP-mannose pyrophophorylase sequences were disclosed in U.S. provisional application Serial No. 60/096,782, filed Aug. 17, 1998, to which the instant application claims priority and which is incorporated herein by reference. The sequences find use in the construction of expression vectors for subsequent transformation into plants of interest, as probes for the isolation of other GDP-mannose pyrophosphorylase-like genes, as molecular markers, and the like.
By xe2x80x9cfragmentxe2x80x9d is intended a portion of the nucleotide sequence or a portion of the amino acid sequence and hence protein encoded thereby. Fragments of a nucleotide sequence may encode protein fragments that retain the biological activity of the native GDP-mannose pyrophosphorylase protein. Alternatively, fragments of a nucleotide sequence that are useful as hybridization probes generally do not encode fragment proteins retaining biological activity. Thus, fragments of a nucleotide sequence may range from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides, and up to the entire nucleotide sequence encoding the GDP-mannose pyrophosphorylase proteins of the invention.
Fragments of the invention include antisense sequences useful in decreasing expression of genes for enzymes of the galactomannan biosynthetic pathway, preferably of GDP-mannose pyrophosphorylase genes. Such antisense fragments may vary in length ranging from at least about 20 nucleotides, about 50 nucleotides, about 100 nucleotides, up to and including the entire coding sequence.
By xe2x80x9cvariantsxe2x80x9d is intended substantially similar sequences. The nucleotide sequences of the invention and the proteins encoded thereby include the native forms as well as variants thereof. For nucleotide sequences, conservative variants include those sequences that, because of the degeneracy of the genetic code, encode the amino acid sequences of galactomannan biosynthetic enzymes, preferably of a GDP-mannose pyrophosphorylase protein. Generally, nucleotide sequence variants of the invention will have 70%-99%, generally, 80%-98%, preferably 90-95% sequence identity to the native nucleotide sequence.
By xe2x80x9cvariantxe2x80x9d protein is intended a protein derived from the native protein by deletion (so-called truncation) or addition of one or more amino acids to the N-terminal and/or C-terminal end of the native protein; deletion or addition of one or more amino acids at one or more sites in the native protein; or substitution of one or more amino acids at one or more sites in the native protein. The variant proteins will be substantially homologous and functionally equivalent to the native proteins. A variant of a native protein is xe2x80x9csubstantially homologousxe2x80x9d to the native protein when about 80%-99%, more preferably about 90%-99%, and most preferably about 95%-99% of its amino acid sequence is identical to the amino acid sequence of the native protein.
By xe2x80x9cfunctionally equivalentxe2x80x9d is intended that the sequence of the variant defines a chain that produces a protein having substantially the same biological effect as the native protein of interest. Thus, for purposes of the present invention, a functionally equivalent variant of GDP-mannose pyrophosphorylase will catalyze the formation of GDP-mannose from mannose-1-phosphate and GTP. Such functionally equivalent variants that comprise substantial sequence variations are also encompassed by the invention. The nucleotide sequences encoding the GDP-mannose pyrophosphorylase proteins of interest can be the naturally occurring sequence cloned from a plant GDP-mannose pyrophosphorylase gene, or they may be synthetically derived sequences. Such variants may result from, for example, genetic polymorphism or from human manipulation. Methods for such manipulations are generally known in the art. For example, amino acid sequence variants of the polypeptide can be prepared by mutations in the cloned DNA sequence encoding the native protein of interest. Methods for mutagenesis and nucleotide sequence alterations are well known in the art. See, for example, Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York); Kunkel (1985) Proc. Natl. Acad. Sci. USA 82:488-492; Kunkel et al. (1987) Methods Enzymol. 154:367-382; Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (Cold Spring Harbor, N.Y.); U.S. Pat. No. 4,873,192; and the references cited therein; herein incorporated by reference. Guidance as to appropriate amino acid substitutions that do not affect biological activity of the protein of interest may be found in the model of Dayhoff et al. (1978) Atlas of Protein Sequence and Structure (Natl. Biomed. Res. Found., Washington, D.C.), herein incorporated by reference. Conservative substitutions, such as exchanging one amino acid with another having similar properties, may be preferred.
In constructing variants of the GDP-mannose pyrophosphorylase protein of interest, modifications to the nucleotide sequences encoding the variants will be made such that variants continue to possess the desired activity. Obviously, any mutations made in the DNA encoding the variant protein must not place the sequence out of reading frame and preferably will not create complementary regions that could produce secondary mRNA structure. See EP Patent Application Publication No. 75,444.
The genes of the galactomannan biosynthetic enzymes of the invention can be optimized for enhanced expression in plants of interest. See, for example, EPA0359472; WO91/16432; Perlak et al. (1991) Proc. Natl. Acad. Sci. USA 88:3324-3328; and Murray et al. (1989) Nucleic Acids Res. 17:477-498. In this manner, the genes can be synthesized utilizing plant-preferred codons. See, for example, Murray et al. (1989) Nucleic Acids Res. 17:477-498, the disclosure of which is incorporated herein by reference. In this manner, synthetic genes can also be made based on the distribution of codons a particular host uses for a particular amino acid. Thus, the nucleotide sequences can be optimized for expression in any plant. It is recognized that all or any part of the gene sequence may be optimized or synthetic. That is, synthetic or partially optimized sequences may also be used.
Alternatively, the sequences of the invention can be used to isolate corresponding sequences in other organisms, particularly other plants. In this manner, methods such as PCR, hybridization, and the like can be used to identify such sequences having substantial sequence similarity to the sequences of the invention. See, for example, Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.) and Innis et al. (1990), PCR Protocols: A Guide to Methods and Applications (Academic Press, New York). Coding sequences isolated based on their sequence identity to the entire maize GDP-mannose pyrophosphorylase coding sequences set forth herein or to fragments thereof are encompassed by the present invention.
In a PCR method, nucleotide primers can be designed based on any 12 to 50 nucleotide stretch, preferably 12-30, nucleotide stretch of contiguous sequence. Pairs of primers can be used in PCR reactions for amplification of DNA sequences from cDNA or genomic DNA extracted from plants of interest. In addition, a single specific primer with a sequence corresponding to one of the nucleotide sequences disclosed herein can be paired with a primer having a sequence of the DNA vector in the cDNA or genomic libraries for PCR amplification of the sequences 5xe2x80x2 or 3xe2x80x2 to the nucleotide sequences disclosed herein. Similarly, nested primers may be used instead of a single specific primer for the purposes of the invention. Methods for designing PCR primers and PCR cloning are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.). See also Ignis et al., eds. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press, New York).
In a hybridization method, the hybridization probes may be genomic DNA fragments, cDNA fragments, RNA fragments, or other oligonucleotides, and may be labeled with a detectable group such as 32P, or any other detectable marker. Probes for hybridization can be made by labeling synthetic oligonucleotides based on the maize GDP-mannose pyrophosphorylase nucleotide sequences of the invention. Preparation of probes for hybridization is generally known in the art and is disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.), hereby incorporated by reference. The labeled probes can be used to screen cDNA or genomic libraries made from plants of interest. Methods for construction of such cDNA and genomic libraries are generally known in the art and are disclosed in Sambrook et al. (1989) Molecular Cloning: A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.).
In hybridization techniques, all or part of the known coding sequence is used as a probe that selectively hybridizes to other possible GDP-mannose pyrophosphorylase coding sequences present in a population of cloned genomic DNA fragments or cDNA fragments (i.e., genomic or cDNA libraries) from a chosen organism. To achieve specific hybridization under a variety of conditions, such probes include sequences that are unique and are preferably at least about 10 nucleotides in length, and most preferably at least about 20 nucleotides in length. Such probes may be used to amplify corresponding GDP-mannose pyrophosphorylase coding sequences from a chosen organism by PCR. This technique may be used to isolate other possible GDP-mannose pyrophosphorylase coding sequences from a desired organism or as a diagnostic assay to determine the presence of a GDP-mannose pyrophosphorylase coding sequence in an organism. Hybridization techniques include hybridization screening of plated DNA libraries (either plaques or colonies; see, e.g., Innis et al., eds. (1990) PCR Protocols: A Guide to Methods and Applications (Academic Press, New York)).
The isolated DNA sequences further comprise DNA sequences isolated from other plants by hybridization with partial sequences obtained from the maize GDP-mannose pyrophosphorylase sequences of the invention. Conditions that will permit other DNA sequences to hybridize to the DNA sequences disclosed herein can be determined in accordance with techniques generally known in the art. For example, hybridization of such sequences may be carried out under conditions of reduced stringency, medium stringency, or high stringency conditions.
The terms xe2x80x9cstringent conditionsxe2x80x9d or xe2x80x9cstringent hybridization conditionsxe2x80x9d includes reference to conditions under which a probe will hybridize to its target sequence, to a detectably greater degree than other sequences (e.g., at least 2-fold over background). Stringent conditions are sequence-dependent and will be different in different circumstances. By controlling the stringency of the hybridization an/or washing conditions, target sequences can be identified which are 100% complementary to the probe (homologous probing). Alternatively, stringency conditions can be adjusted to allow some mismatching in sequences so that lower degrees of similarity are detected (heterologous probing). Generally, a probe is less than about 1000 nucleotides in length, preferably less than 500 nucleotides in length.
Typically, stringent conditions will be those in which the salt concentration is less than about 1.5 M Na ion, typically about 0.01 to 1.0 M Na ion concentration (or other salts) at pH 7.0 to 8.3 and the temperature is at least about 30xc2x0 C. for short probes (e.g., 10 to 50 nucleotides) and at least about 60xc2x0 C. for long probes (e.g., greater than 50 nucleotides). Stringent conditions may also be achieved with the addition of destabilizing agents such as formamide. By xe2x80x9clow stringency conditionsxe2x80x9d is meant hybridization with a buffer solution of 30% formamide, 1 M NaCl, 1% SDS(sodium dodecyl sulphate) at 37xc2x0 C., and a wash in 2xc3x97SSC (20xc3x97SSC=3.0 M NaCl/0.3 M trisodium citrate) at 50xc2x0 C. By xe2x80x9cmoderate stringency conditionsxe2x80x9d is meant hybridization in 40% formamide, 1 M NaCl, 1% SDS at 37xc2x0 C., and a wash in 1xc3x97SSC at 60xc2x0 C. By xe2x80x9chigh stringency conditionsxe2x80x9d is meant hybridization in 50% formamide, 1 M NaCl, 1% SDS at 37xc2x0 C., and a wash in 0.1xc3x97SSC at 60 to 65xc2x0 C.
Specificity is typically the function of post-hybridization washes, the critical factors being the ionic strength and temperature of the final wash solution. For DNA-DNA hybrids, the Tm can be approximated from the equation of Meinkoth and Wahl, Anal. Biochem 138:267-284 91984): Tm=81.5xc2x0 C.+16.6 (log M)+0.41 (%GC)xe2x88x920.61 (% form)xe2x88x92500/L; where M is the molarity of monovalent cations, %GC is the percentage of guanosine and cytosine nucleotides in the DNA, % form is the percentage of formamide in the hybridization solution, and L is the length of the hybrid in base pairs. The Tm is the temperature (under defined ionic strength and pH) at which 50% of a complementary target sequence hybridizes to a perfectly matched probe. Tm is reduced by about 1xc2x0 C. for each 1% of mismatching; thus, Tm, hybridization and/or wash conditions can be adjusted to hybridize to sequences of the desired identity. For example, if sequence with xe2x89xa790% identity are sought, the Tm can be decreased 10xc2x0 C. Generally, stringent conditions are selected to be about 5xc2x0 C. lower than the thermal melting point (Tm) for the specific sequence and its complement at a defined ionic strength and pH. However, severely stringent conditions can utilize a hybridization and/or wash at 1, 2, 3, or 4xc2x0 C. lower than the thermal melting point (Tm); moderately stringent conditions can utilize a hybridization and/or wash at 6, 7, 8, 9, or 10xc2x0 C. lower than the thermal melting point (Tm); low stringency conditions can utilize a hybridization and/or wash at 11, 12, 13, 14, 15, or 20xc2x0 C. lower than the thermal melting point (Tm). Using the equation, hybridization and wash compositions, and desired Tm, those of ordinary skill will understand that variations in the stringency of hybridization and/or wash solutions are inherently described. If the desired degree of mismatching results in a Tm of less than 45xc2x0 C. (aqueous solution) or 32xc2x0 C. (formamide solution) it is preferred to increase the SSC concentration so that a higher temperature can be used. An extensive guide to the hybridization of nucleic acids is found in Tijssen, Laboratory Techniques in Biochemistry and Molecular Biologyxe2x80x94Hybridization with Nucleic Acid Probes, Part I, Chapter 2 xe2x80x9cOverview of principles of hybridization and the strategy of nucleic acid probe assaysxe2x80x9d, Elsevier, N.Y. (1993); and Current Protocols in Molecular Biology, Chapter 2, Ausubel, et al., Eds., Greene Publishing and Wiley-Interscience, New York (1995).
In general, sequences that confer GDP-mannose pyrophosphorylase activity and hybridize to the reference DNA sequences disclosed herein will have at least 70%, at least 75%, at least 80%, at least 85%, at least 90% and most preferably about 95-100% sequence identity to the reference GDP-mannose pyrophosphorylase sequences of the present invention.
Methods of alignment of sequences for comparison are well-known in the art. For example, optimal alignment of sequences for comparison may be conducted by the local homology algorithm of Smith and Waterman (1981) Adv. Appl. Math. 2:482; by the homology alignment algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48:443; and by the search for similarity method of Pearson and Lipman (1988) Proc. Natl. Acad. Sci. 85:2444. For the purposes of the instant invention, sequence identity is determined by the GAP program, version 10 in the Wisconsin Genetics Software Package, Genetics Computer Groups (GCG) (575 Science Drive, Madison, Wis.) using the default settings. See, Ausubel et al., eds. (1995) Current Protocols in Molecular Biology, Chapter 19 (Greene Publishing and Wiley-Interscience, New York).
The sequences of the invention are useful to transform plants and manipulate the levels of the enzymes of the galactomannan biosynthetic pathway, preferably of GDP-mannose pyrophosphorylase in the transformed plant. Such manipulation provides the ability to up-regulate or down-regulate the production of the gum galactomannan and/or of substrates in the galactomannan biosynthetic pathway such as GDP-mannose. Toward this end, the sequences of the invention may be utilized in expression cassettes with either constitutive or tissue-specific promoters.
Constitutive promoters would provide a constant supply of one or more enzymes of the galactomannan biosynthetic pathway throughout the plant. Alternatively, a constitutive promoter driving the expression of antisense RNA to an mRNA of the galactomman biosynthetic pathway would result in a decrease in an enzyme of the galactomannan pathway, and a concomitant decrease in gum production. Furthermore, constitutive expression of an antisense RNA to a GDP-mannose pyrophosphorylase mRNA would result in a decrease in GDP-mannose, a precursor of protein glycosylation, inhibit cell growth or cause cell death. Such constitutive promoters include, for example, the core promoter of the Rsyn7 (copending U.S. patent application Ser. No. 08/661,601); the promoter for the small subunit of ribulose-1,5-bis-phosphate carboxylase; promoters from tumor-inducing plasmids of Agrobacterium tumefaciens; such as the nopaline synthase and octopine synthase promoters; and viral promoters such as the cauliflower mosaic virus (CaMV) 19S and 35S promoters; the figwort mosaic virus 35S promoter, the rice actin promoter (McElroy et al. (1990) Plant Cell 2:163-171); the ubiquitin promoter (Christensen et al. (1989) Plant Mol. Biol. 12:619-632 and Christensen et al. (1992) Plant Mol. Biol. 18:675-689); pEMU (Last et al. (1991) Theor. Appl. Genet. 81:581-588); the MAS promoter (Velten et al (1984) EMBO J. 3:2723-2730); the ALS promoter (U.S. patent application Ser. No. 08/409,297), and the like. Other constitutive promoters include, for example, U.S. Pat. Nos. 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; and 5,608,142. For beans, Scp1 is a preferred constitutive promoter.
Alternatively, it may be desired to express an enzyme of the galactomannon biosynthetic pathway in a tissue-specific manner. Thus tissue-specific promoters, particularly seed-preferred promoters may be used. Examples of tissue-specific promoters include seed-preferred, leaf-specific, and tassel-specific promoters. Seed-preferred promoters include both seed-specific promoters (those promoters active during seed development such as promoters of seed storage proteins) as well as seed-germinating promoters (those promoters active during seed germination). See Thompson et at, (1 989) BioEssays 10: 108, incorporated herein in its entirety by reference. Such seed-preferred promoters include, but are not limited to, Cim1 (cytokinin-induced message); cZ19B1 (maize 19KDa zein); and celA (cellulose synthase). Gama-zein is a preferred endosperm-specific promoter. Glob-1 is a preferred embryo-specific promoter. For dicots, seed-specific promoters include, but are not limited to, bean b-phaseolin, napin, xcex2-conglycinin, soybean lectin, and the like. For monocots, seed-specific promoters include, but are not limited to, maize 15 kD zein, 22 kD zein, 27 kD zein, g-zein, waxy, shrunken 1, shrunken 2, globulin 1, etc. Leaf-specific promoters include, Yamamoto et al. (1997) Plant J. 12(2):255-265; Kawamata et a. (1997) Plant Cell Physiol. 38(7):792-803; Hansen et at (1997) Mol. Gen. Genet. 254(3):337-343; Russell et al (1997) Transgenic Res. 6(2):157-168; Rinehart et al (1996) Plant Physiol. 112(3):1331-1341; Van Camp et al. (1996) Plant Physiol. 112(2):525-535; Canevascini et al. (1996) Plant Physiol. 112(2):513-524; Yamamoto et al. (1994) Plant Cell Physiol. 35(5):773-778; Lam (1994) Results Probl. Cell Differ. 20:181-196; Orozco et al. (1993) Plant Mol. Biol. 23(6): 1129-1138; Matsuoka et al. (1993) Proc. Natl. Acad. Sci. USA 90(20):9586-9590; and Guevara-Garcia et al (1993) Plant J. 4(3):495-505. However, other promoters useful in the practice of the invention are known to those of skill in the art.
Tissue-specific promoters may also be use to express antisense RNAs to mRNAs of the galactomannan biosynthetic pathway. In one embodiment, a tissue-specific and inducible promoter is used to drive expression of an antisense RNA to a GDP-mannose pyrophosphorylase mRNA. Induction of the anti-sense RNA in a specific tissue to result in the inhibition of growth of that tissue. Such induction would be useful to inhibit the growth of a plant tissue after it has performed its function, yet continues to draw on the energy resources of the plant for its maintenance. An example of this tissue type is corn tassel.
The sequences of the invention may be used in expression cassettes for expression in any plant of interest. Where expression cassettes are needed, such expression cassettes will comprise a transcriptional initiation region linked to the coding sequence or antisense sequence of the nucleotide of interest. Such an expression cassette is provided with a plurality of restriction sites for insertion of the sequence to be under the transcriptional regulation of the regulatory regions. The expression cassette may additionally contain selectable marker genes.
The transcriptional initiation region, the promoter, may be native or analogous or foreign or heterologous to the plant host. By foreign is intended that the transcriptional initiation region is not found in the native plant into which the transcriptional initiation region is introduced. As used herein, xe2x80x9cheterologousxe2x80x9d in reference to a nucleic acid is a nucleic acid that originates from a foreign species, or, if from the same species, is substantially modified from its native form in composition and/or genomic locus by deliberate human intervention. For example, a promoter operably linked to a heterologous structural gene is from a species different from that from which the structural gene was derived, or, if from the same species, one or both are substantially modified from their original form. A heterologous protein may originate from a foreign species or, if from the same species, is substantially modified from its original form by deliberate human intervention. Additionally, the promoter may be the natural sequence or alternatively a synthetic sequence. As used herein a chimeric gene comprises a coding sequence operably linked to a transcription initiation region that is heterologous to the coding sequence.
The transcriptional cassette will include in the 5xe2x80x2-to-3xe2x80x2 direction of transcription, a transcriptional and translational initiation region, a DNA sequence of interest, and a transcriptional and translational termination region functional in plants. The termination region may be native with the transcriptional initiation region, may be native with the DNA sequence of interest, or may be derived from another source. Convenient termination regions are available from the Ti-plasmid of A. tumefaciens, such as the octopine synthase and nopaline synthase termination regions. See also Guerineau et al. (1991) Mol. Gen. Genet. 262:141-144; Proudfoot (1991) Cell 64:671-674; Sanfacon et al. (1991) Genes Dev. 5:141-149; Mogen et al. (1990) Plant Cell. 2:1261-1272; Munroe et al. (1990) Gene 91: 151-158; Ballas et al. (1989) Nucleic Acids Res. 17:7891-7903; Joshi et al. (1987) Nucleic Acids Res. 15:9627-9639.
Nucleotide sequences of the invention are provided in expression cassettes for expression in the plant of interest. The cassette will include 5xe2x80x2 and 3xe2x80x2 regulatory sequences operably linked to the sequence of interest. The cassette may additionally contain at least one additional sequence to be co-transformed into the organism. Alternatively, the additional sequence(s) can be provided on another expression cassette.
In preparing the expression cassette, the various DNA fragments may be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers may be employed to join the DNA fragments or other manipulations may be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, or the like. For this purpose, in vitro mutagenesis, primer repair, restriction, annealing, resubstitutions, e.g., transitions and transversions, may be involved.
The sequences of the present invention can be used to transform or transfect any plant. In this manner, genetically modified plants, plant cells, plant tissue, seed, and the like can be obtained. Plants of particular interest include grain plants which provide seeds of interest, oil seed plants and leguminous plants. Seeds of interest include grain seeds, such as corn, wheat, barley, rice, sorghum, rye, etc. Oil seed plants include cotton, soybean, safflower, sunflower, Brassica, alfalfa, etc. Leguminous plants include beans and peas. Beans include guar, locust bean, fenugreek, soybean, garden beans, cowpea, mungbean, lima bean, fava bean, lentils, chickpea, etc.
Transformation protocols as well as protocols for introducing nucleotide sequences into plants may vary depending on the type of plant or plant cell, i.e. monocot or dicot, targeted for transformation. Suitable methods of introducing nucleotide sequences into plant cells and subsequent insertion into the plant genome include microinjection (Crossway et al. (1986) Biotechniques 4:320-334), electroporation (Riggs et al. (1986) Proc. Natl. Acad. Sci. USA 83:5602-5606, Agrobacterium-mediated transformation (U.S. Pat. No. 5,563,055), direct gene transfer (Paszkowski et al. (1984) EMBO J. 3:2717-2722), and ballistic particle acceleration (see, for example, Sanford et al, U.S. Pat. No. 4,945,050; Tomes et al. (1995) xe2x80x9cDirect DNA Transfer into Intact Plant Cells via Microprojectile Bombardment,xe2x80x9d in Plant Cell, Tissue, and Organ Culture: Fundamental Methods, ed. Gamborg and Phillips (Springer-Verlag, Berlin); and McCabe et al. (1988) Biotechnology 6:923-926). Also see Weissinger et al. (1988) Annual Rev. Genet. 22:421-477; Sanford et al. (1987) Particulate Science and Technology 5:27-37 (onion); Christou et al. (1988) Plant Physiol. 87:671-674 (soybean); McCabe et al. (1988) Bio/Technology 6:923-926 (soybean); Finer and McMullen (1991) In Vitro Cell Dev. Biol. 27P: 175-182 (soybean); Singh et al. (1998) Theor. Appl. Genet. 96:319-324 (soybean); Datta et al. ( 1990) Biotechnology 8:736-740 (rice); Klein et al. (1988) Proc. Natl. Acad. Sci. USA 85:4305-4309 (maize); Klein et al. (1988) Biotechnology 6:559-563 (maize); Klein et al. (1988) Plant Physiol. 91:440-444 (maize); Fromm et al. (1990) Biotechnology 8:833-839 (maize); Hooydaas-Van Slogteren and Hooykaas (1984) Nature (London) 311:763-764; Bytebier et al. (1987) Proc. Natl. Acad. Sci. USA 84:5345-5349 (Liliaceae); De Wet et al. (1985) in The Experimental Manipulation of Ovule Tissues, ed. Chapman et al. (Longman, N.Y.), pp. 197-209 (pollen); Kaeppler et al. (1990) Plant Cell Reports 9:415-418; and Kaeppler et al. (1992) Theor. Appl. Genet. 84:560-566 (whisker-mediated transformation); D""Halluin et al. (1992) Plant Cell 4:1495-1505 (electroporation); Li et al. (1993) Plant Cell Reports 12:250-255 and Christou and Ford (1995) Annals of Botany 75:407-413 (rice); Osjoda et al. (1996) Nature Biotechnology 14:745-750 (maize via Agrobacterium tumefaciens); all of which are herein incorporated by reference.
Plant cells expressing GDP-mannose pyrophosphorylase may be detected by a variety of methods known to those skilled in the art. See, for example, Szumilo et al., (1993) J. Biol. Chem. 268:17943-17950, the contents of which are incorporated by reference. Such assays include Northern assays for the detection of GDP-mannose pyrophosphorylase mRNA (See Sambrook et al. (1989) A Laboratory Manual (2d ed., Cold Spring Harbor Laboratory Press, Plainview, N.Y.)); enzymatic assays for GDP-mannose pyrophosphorylase activity and assays for levels of GDP-mannose.
The modified plant may be grown into plants in accordance with conventional ways. See, for example, McCormick et al. (1986) Plant Cell. Reports 5:81-84. These plants may then be grown, and either pollinated with the same transformed strain or different strains, and the resulting hybrid having the desired phenotypic characteristic identified. Two or more generations may be grown to ensure that the subject phenotypic characteristic is stably maintained and inherited and then seeds harvested to ensure the desired phenotype or other property has been achieved.